The present invention relates to a fuel injection control system for an internal combustion engine having an electronic control system such as a microcomputer.
A fuel injection control system having a microcomputer is widely used in a four-cycle engine.
A recent two-cycle engine is also equipped with an electronic control system for controlling various components of the engine, such as fuel injectors. Japanese Patent Application Laid-Open 63-255543 discloses such an electronic fuel injection control system for the engine. The system has a main intake pipe for inducing fresh air into a crankcase and a sub intake pipe for directly inducing fresh air into the crankcase. A fuel injector is provided in each of the intake pipes. An electronic control unit is provided for controlling the injection timing and quantity of fuel injected from the fuel injector
Japanese Patent Application Laid-Open 63-29039 discloses a system in which the quantity of intake air Q is derived from a look-up table in accordance with throttle valve opening degree .alpha. and engine speed N as parameters for calculating a basic fuel injection quantity Tp. Fuel injection quantity is calculated by correcting the basic fuel injection quantity with various correcting quantities in accordance with engine operating conditions. In general, the engine speed N is calculated from output data detected by a speed sensor such as a crank angle sensor and the fuel injection is controlled in synchronism with the crank angle.
When an ignition switch is turned off to stop the engine, the fuel injection operation of the fuel injector stops and a fuel pump stops supplying the fuel.
However, if the fuel injector operates so as to inject fuel after the stopping of supplying the fuel because of a delay of stopping the energization of the fuel injector, the fuel pressure in the fuel supply passage drops. Therefore, if the engine is restarted in such a state, although, the fuel pump starts to supply fuel to the injector, the fuel pressure does not increase immediately. Consequently, the quantity of injected fuel is small because of the low fuel pressure, causing a poor starting characteristic of the engine.